In recent years, a light emitting diode (LED) lamp has been undergoing a rapid growth and gradually stepping into the general illumination market. Compared with a conventional incandescent tungsten filament bulb and a fluorescent lamp, a LED lamp makes use of the superiority in small size, energy-saving, environment-friendly and long lifespan to achieve an appellation of green light source.
Referring to FIG. 1, a structural view of a related optical lens applied in a LED lamp. As shown in FIG. 1, an optical lens 10 includes a mounting pedestal/base 11, a dome structure 13 disposed on the mounting base 11, and a protrusion structure 15 outwardly protruding from the dome structure 13 along a direction away from the mounting base 11. The dome structure 13 has a first optical curved surface 131, the protrusion structure 15 has a second optical curved surface 151, and a boundary line of the second optical curved surface 151 and the first optical curved surface 131 is a horizontal line and disposed at an external surface (i.e., the first optical curved surface 131) of the dome structure 13.
Referring to FIG. 2, it is a light pattern simulation diagram of the optical lens 10 as shown in FIG. 1. As seen from FIG. 2, it can be found that a dark band appears in the middle of the light pattern and is marked by an oval dashed box, that is, a local uniformity of light distribution of the optical lens is poor.